The invention relates to a method for comminuting chips in a comminuting space between a driven horizontal shaft, which can be rotated in both directions and is fitted with shearing elements, and assigned counter-shearing elements, with chips introduced from above being comminuted and discharged downwards via a perforated screening plate and blocking constituents, which cause the shaft to come to a standstill, being segregated after reversing the shaft. The invention also relates to two apparatuses for carrying out the method according to the invention.
The comminuting of chips in horizontal chip breakers is known from DE 94 18 904 U1. In this case, chips which are generated during the machining of workpieces made of metal, plastic or wood are comminuted in a comminuting space between two electrically driven shafts, the shearing cutters of which engage in one another during rotation, and are discharged via a perforated plate. If a coarse part becomes lodged between the two shafts, and consequently causes a standstill of the shafts, the shafts can be moved in the opposite direction of rotation by means of a corresponding controller. A blocking coarse part can then generally be removed by hand or magnetic parts can be removed by magnets from the comminuting space. Each time coarse parts are removed, standstills and consequently reduced throughput rates occur. Moreover, the use of personnel is necessary for this.
A vertical chip breaker for steel or metal chips with a coarse-part ejecting element is known from EP 0 717 663 B1. This single-shaft breaker comprises a receiving hopper and a downwardly adjoining grinding hopper with circumferentially distributed tearing blocks, past the tearing edges of which the tearing cutters attached to a rotating cutter head can be moved. Underneath the grinding hopper there adjoins a grinding mechanism. Provided in the lower region of the grinding hopper is a discharge channel for coarse parts, which can be opened by means of a powered channel slide. If there is a coarse part among the chip material, it lies on the grinding mechanism and is moved by the cutter head together with the chips in a rotating manner until blocking of the cutter head occurs. To eliminate the blockage, a slow reversing operation is initiated and the coarse-part ejecting element is opened, in order that the disruptive elements can be transported from the cutter head towards the discharge and through the latter.
A disadvantage of this configuration is that it cannot be used for horizontal chip breakers. Furthermore, if there is an impairment of the rotational movement of the cutter head, there is no differentiation here between dense clumps of chips and coarse parts or combinations of the two. Experience has shown that dense clumps of chips can also often lead to a blockage. These clumps are likewise removed here via the discharge and are consequently extracted from the comminuting operation.
The object of the present invention is consequently to provide a method and two apparatuses of the type mentioned at the beginning, including a horizontal chip breaker which differentiates the blocking constituents according to groups, for example dense clumps of chips or purely coarse parts, and assigns to each group a defined reversing operation and, if appropriate, discharge from the comminuting space by means of a coarse-part ejecting element.
To achieve the object, the invention provides a method in which the rate of change of the loading of the driven shaft fitted with shearing elements is sensed, the presence of blocking constituents being established on the basis of the sensed rate of change of the loading while taking into account the type, quantity and/or size of chip, and then the non-comminuted blocking constituents being ejected after one or more reversals of the shaft. When sensing the rate of change of the loading of the shaft fitted with shearing elements due to blocking constituents it is found that each type of constituent brings about a different rate of change of the loading. Hard, one-piece coarse parts, for example fragments of machined workpieces, produce a high rate of change of the loading. Very dense clumps of chips bring about a lower rate of change of the loading. For less dense clumps of chips, the value is lower still. At the same time, the various chip parameters have to be taken into account, since chips break more or less easily, depending for example on the material from which they are produced. If there is an operational disruption as a result of a blocking part, it can be automatically discharged by means of a coarse-part ejecting element by one or more reversing operations. Intervention by the operator is not necessary. The comminuting operation is continued again after the removal. For configurations in which the counter-shearing elements are attached on a second shaft, it may be advantageous to program the controllers of the shaft and countershaft in such a way that during the reversing operation one shaft is stationary or is reversed much more slowly than the other shaft. This counteracts any throwing out of the previously blocking constituents. Furthermore, it is more probable in such a sequence of movements that the blocking constituents are taken along by the faster shaft, and consequently are taken to the same side of the comminuting space.
The method according to the invention may be carried out in an advantageous way by sensing the acceleration of the shaft to sense the rate of change of the loading of the driven shaft fitted with shearing elements. Hard, one-piece coarse parts, for example fragments of machined workpieces, produce a high negative acceleration. Very dense clumps of chips bring about a lower negative acceleration. For less dense clumps of chips, the value is lower still. It goes without saying that the rate of change of the loading can also be sensed for example via the change in torque of the shaft by means of strain gauges. Depending on the load, in this case the rate of speed of deformation of the shaft would vary. Vibration-measuring instruments are also conceivable, since a blockage due to coarse parts would cause greater vibration than dense clumps of chips.
The method according to the invention may be carried out in such a way that, on the basis of the established acceleration profile, the constituents causing a blockage are subdivided into at least two categories, the constituents being moved more or less frequently by reversing of the shaft, and either passed on in a comminuted state or thrown back in an uncomminuted state, according to the relevant category.
Subdivision into categories allows an optimized program sequence to be devised for each type of constituent in the case of blocking constituents. For instance, compacted clumps of chips which cause blocking can be recognized as such on the basis of the relatively low negative acceleration caused by them. Sustained repeated reversing with a closed coarse-part ejecting element may follow, intended to comminute the compacted clump of chips. At the end of the reversing operation, however, still existing dense remains of clumps can be discharged by means of the openable coarse-part ejecting element. Blocking coarse parts form another category. Coarse parts may be, for example, fragments of machined workpieces or screws. These coarse parts abruptly bring about a high negative acceleration when there is a blockage. Since it is not possible for constituents of this type to be comminuted by the shearing elements, a short reversing operation with the coarse-part ejecting element open is initiated in order to eject the coarse part as quickly as possible.
It may be advantageous in the case of the method according to the invention to arrange the categories according to increasing negative acceleration, the frequency of reversal decreasing from category to category with increasing negative acceleration. The more solid a blocking constituent is, the higher the negative acceleration in the case of a blockage and the lower the probability of this constituent being comminuted by frequent reversal and of the blockage being ended. It is therefore advisable in the case of solid objects to end the blockage by reversing briefly and subsequently segregating the constituent by means of the coarse-part ejecting element, so that the chip comminution can be continued without delay.
The method according to the invention may also be advantageously carried out in such a way that the change in rotational speed of the drive is measured for sensing a negative shaft acceleration. By sensing the negative shaft acceleration via the change in speed of the drive, there is no need for direct sensing at the shaft. Sensing at the shaft could only be accomplished with great effort. For example, a sensor would have to be protected against becoming soiled by chip dusts adhering to it or penetrating into the housing. An optical sensor could not be used on account of the chips to be comminuted.
Finally, the method according to the invention may also be carried out in such a way that the rotational speed is set to be lower during the reversing of the shaft than the normal rotational speed. Reducing the speed during reversing prevents blocking constituents from being dislodged abruptly and thrown about in the comminuting space. Instead of this, the intention is for the blocking constituent to be carefully dislodged and taken beyond the shaft to the coarse-part ejecting element by reversing.
In the case of a first apparatus for comminuting chips which is equipped with a horizontal shaft which is arranged in a comminuting space, can be rotated in both directions by means of a drive and controller and is fitted with shearing elements, with counter-shearing elements assigned to this shaft and with a curved perforated screening plate adapted to the shape of the shaft, the object stated above is achieved by an openable coarse-part ejecting element being attached to the walls of the comminuting space lying parallel to the shaft axis and by the counter-shearing elements being arranged in two rows on walls of the comminuting space lying parallel to the shaft axis. Furthermore, a controller for the coarse-part ejecting element is provided, the controllers of the shaft and coarse-part ejecting element being linked with each other. For sensing the rate of change of the loading of the shaft, a controller for the coarse-part ejecting element is provided, sensing the negative accelerations of the shaft, and, depending on the respective negative acceleration, a variable number of reversing operations with the coarse-part ejecting element closed and/or open can be programmed.
The first apparatus according to the invention, i.e. the horizontal single-shaft breaker, makes it possible for the comminuting operation to proceed with virtually no friction. A separation of hard parts and chips takes place. Any discharge of chips via the coarse-part ejecting element is avoided to the greatest extent. The standstill times become shorter and wearing of the shearing elements is reduced. The apparatus operates automatically, which reduces the demand for labour. The apparatus can be produced simply and inexpensively. It is possible to retrofit existing breakers correspondingly, or in the production of new breakers to fall back on already existing modules to the greatest extent. For instance, it is conceivable for a simple flap which can be opened outwards to be used as the coarse-part ejecting element. However, it may also be a door to be pushed to the side.
It may be advantageous to design the first apparatus according to the invention in such a way that the negative accelerations of the shaft can be determined by sensing measured values at the drive. The drive of a chip breaker is normally arranged outside the chip breaker, so that a measuring device can be accommodated there in a dustfree environment and can be serviced easily.
It may be advantageous to design the first apparatus according to the invention in such a way that one of the shearing rows lies at the height of the shaft axis or lower, i.e. underneath the opening of the coarse-part ejecting element, and the other shearing row is arranged on the opposite wall above the shaft axis. If a constituent becomes lodged between the lower shearing row and the shaft, reversing once can loosen this constituent and move it directly to the opening in the wall, whereby it leaves the comminuting space. On the opposite side, the shearing row should be attached at a higher level, in order that a blocking constituent which has to be transported to the coarse-part ejecting element can be transported more easily beyond the shaft.
Furthermore, it may be advantageous to design the first apparatus according to the invention in such a way that the lower-lying shearing row is the lower limitation of the coarse-part ejecting element. Such an embodiment has the effect that a blocking constituent is already as close as possible to the coarse-part ejecting element. Brief reversing is sufficient to loosen this constituent and segregate it immediately.
The first apparatus according to the invention may be advantageously designed in such a way that the shearing rows are mounted on the walls with a slope towards the coarse-part ejecting element. Such a slope facilitates the transport of blocking constituents to the coarse-part ejecting element and through it during reversing.
In the case of a second apparatus for comminuting chips which is equipped with a horizontal shaft which is arranged in a comminuting space, can be rotated in both directions by means of a drive and controller and is fitted with shearing elements and with counter-shearing elements arranged on an assigned countershaft of the same kind and with a perforated screening plate curved to match the shaft and countershaft, the object stated above is achieved by an openable coarse-part ejecting element being attached to at least one of the walls of the comminuting space lying parallel to the shaft axis. Furthermore, for sensing the rate of change of the loading of the driven shaft(s), a controller for the coarse-part ejecting element is provided, sensing the negative accelerations of at least one of the shafts, the controllers of the shaft, countershaft and coarse-part ejecting element being linked with each other; at the same time, depending on the respective negative acceleration, a variable number of reversing operations with the coarse-part ejecting element closed and/or open can be programmed.
The second apparatus according to the invention, i.e. the horizontal twin-shaft breaker, makes it possible for the comminuting operation to proceed with no friction. In precisely the same way as in the case of the first apparatus according to the invention, i.e. the single-shaft breaker, a virtually complete separation of hard parts and chips takes place, any discharge of chips via the coarse-part ejecting element being avoided to the greatest extent. The standstill times become shorter and wearing of the shearing shafts is reduced. This apparatus also operates automatically and can be produced simply and inexpensively. It is possible to retrofit existing twin-shaft breakers correspondingly, or in the production of new breakers to fall back on already existing modules to the greatest extent. One or two coarse-part ejecting elements may be provided, for example in the form of flaps or sliding doors.
It may be advantageous to design the second apparatus according to the invention, i.e. the twin-shaft chip breaker, in such a way that the negative accelerations of at least one of the shafts can be determined by sensing measured values at the drive. The drive of a chip breaker is normally arranged outside the chip breaker, so that a measuring device can be accommodated there in a dustfree environment and can be serviced easily.
It may be advantageous to design the second apparatus according to the invention, i.e. the twin-shaft chip breaker, in such a way that the shaft is mounted at a higher level than the countershaft and a coarse-part ejecting element is attached on the wall facing the countershaft. The higher-level mounting of the shaft has the effect that the previously blocking constituents are more likely to be carried by the lower-mounted countershaft to the coarse-part ejecting element. This reduces the number of reversals required, and also makes it possible to dispense with a second coarse-part ejecting element.
Furthermore, it may be advantageous to design both apparatuses according to the invention, i.e. the single-shaft and twin-shaft breakers, in such a way that the apparatus is set up with an angle of inclination about one or two axes. In this case, it may also be advantageous that the one angle of inclination or both angles of inclination can be individually set. In one embodiment, in which for example the axis of rotation of the inclination is formed parallel to the axes of rotation of the shafts, the ejecting of coarse parts can be facilitated significantly by an oblique position of the apparatus towards the coarse-part ejecting element.
Furthermore, it may be advantageous for both apparatuses according to the invention to fasten the shearing elements and/or counter-shearing elements individually on the shaft. During the comminution of chips, there is irregular wearing of the (counter-) shearing elements. Some (counter-) shearing elements are worn away more quickly than others. These (counter-) shearing elements can then be removed and renewed individually.
It may also be advantageous for both apparatuses according to the invention to form the shearing elements and/or counter-shearing elements on a shaft differently. For instance, a shaft, or both shafts, may be fitted with differently sharp (counter-) shearing elements. The sharper (counter-) shearing elements may be arranged at the regions of greater stress. In the case of an arrangement with a shaft axis inclined slightly in the direction of gravitation, it is advisable for example to fit increasingly sharper (counter-) shearing elements from the higher end of the shaft to the lower end of the shaft.
Both apparatuses may be advantageously equipped with a drive in the form of an electric motor or hydraulic motor.
If they are provided with an electric motor, to sense the negative shaft acceleration it may be advantageous for both apparatuses to provide a pulse pickup for measuring the rotational speed at the electric motor. In this case, a signal disc, in the form of a rotor, with a proximity switch may be used as the pulse pickup. By sensing the negative shaft acceleration via the change in rotational speed of the drive, there is no need for direct registration at the shaft, which could also only be accomplished with great effort.
Furthermore, if they are provided with an electric motor, it may be advantageous for both apparatuses to measure the negative shaft acceleration via the increase in current.
If they are provided with a hydraulic motor, it may also be advantageous for both apparatuses to sense the negative shaft acceleration via a volumetric flow measurement or rotational speed measurement.
Furthermore, it may be advantageous to design the apparatuses according to the invention in such a way that the coarse-part ejecting element is equipped with a sensor for sensing passing coarse parts. In this case, the sensor may be an optical sensor. If a constituent passes the coarse-part ejecting element, directly after that the coarse-part ejecting element is closed and the reversing operation is ended.
The apparatuses according to the invention may be advantageously designed in such a way that the coarse-part ejecting element is a flap which can be opened by means of pneumatics or hydraulics. Flaps operated in this way are already known from and successfully proven in other areas. An ejecting element in the form of a flap can be produced simply and at low cost. This embodiment is also robust enough with respect to the daily demands of the comminuting operation.